1. Field of the Invention
This invention relates to a fin stabilizer system for counteracting roll and/or list or side away of a ship at sea.
2. Description of the Prior Art
U.S. Pat. No. 3,756,262 discloses a known stabilizer system for counteracting roll while a ship is under way. In this type of system, the rate of vessel roll is sensed by a hydraulically driven rate gyroscope. The gyroscope generates differential hydraulic pressure control signals which are used to adjust external submerged fin stabilizers. While such systems have proven to be highly effective in counteracting roll, they lack the capability of also detecting and effectively counteracting list and side sway.
Other known systems of the type disclosed for example in U.S. Pat. No. 3,897,717 employ pendulum type sensors to detect changes in the attitude of a structure such as for example an instrument platform. In this type of system, the pendulum swings between and serves as a common obstructing member for a pair of confronting flow restrictors. The restrictors are fixed in relation to the structure and are incorporated into a hydraulic control circuit connected to a hydraulic linear actuator. The linear actuator is mechanically connected to the platform and operates in response to control signals from the pendulum type sensor. As long as the structure remains properly oriented, the pendulum remains centrally positioned between the restrictors, the hydraulic pressure across the restrictors remains in balance and the linear actuator remains passive. In the event that the structure undergoes an undesirable change in attitude, the positions of the restrictors will change in relation to the relatively stationary pendulum, thereby upsetting the balance of hydraulic fluid flow therethrough. The resulting differential fluid pressure serves as a control signal which operates the actuator to return the structure to the desired attitude. This type of system is effective in counteracting very gradual changes in attitude, e.g., listing or side sway of a ship at sea, but is incapable of effectively counteracting rolling due to the fact that the corrective action derived from the pendulum sensor is always 90.degree. out of phase with each change in the direction of roll.
The basic objective of the present invention is to provide an improved fin stabilizer system having the capability of counteracting vessel roll and/or list or side sway conditions.